Help with cars

Hello guys

I want to make that when I spawn for example a /car infernus and get out of it and spawn cheetah,but the infernus to be deleted

Example: I spawned infernus then I got off it and spawned cheetah,I wNt that cheetah to be spawned and my infernus to be removed

Bcz when i type /infernus it spawn a car everytime I type it so it is a mess

-------

Also

I want that when u driving a car and try to get another car while u r in it, it rejects the cmd and show u: you arr already drvig a car, get off and try again

--------

[reps] for any help